1. Field of the Invention
This invention relates to an air conditioner having a refrigerant heater.
2. Description of the Related Art
A conventional heat-pump air conditioner has the drawback that the heating capacity decreases as the outdoor temperature falls. An air conditioner having a refrigerant heater is known, which overcomes the drawback and in which a refrigerant heater such as a gas burner heats the refrigerant and cooperates with a heat pump to perform heating operation.
The air conditioner of the conventional type having a refrigerant heater will be described with reference to FIG. 1. As shown in FIG. 1, the air conditioner has a refrigeration circuit including compressor 1, four-way valve 2, outdoor heat exchanger 3, check valve 4, expansion valve 5, indoor heat exchanger 6, and check valve 7, all connected in this order by pipes. Electromagnetic valve 8 and refrigerant heater 9 are connected by pipes and arranged between the refrigerant suction pipe of compressor 1, on one side, and the node connecting check valve 4 and expansion valve 5, on the other side.
Refrigerant heater 9 has gas burner 10 for heating the refrigerant. Gas burner 10 is connected to the fuel source (not shown) by proportional control valve 11.
Outdoor fan 12 for circulating the outdoor air is arranged near outdoor heat exchanger 3, and indoor fan 13 for circulating the indoor air is arranged near indoor heat exchanger 6.
During cooling operation, compressor 1 is activated while electromagnetic valve 8 is closed. As a result, the refrigerant flows in the direction indicated by the solid-line arrows, outdoor heat exchanger 3 functioning as a condenser, and indoor heat exchanger 6 as an evaporator.
During heating operation, compressor 1 is activated and four-way valve 2 is switched while electromagnetic valve 8 is opened. In addition, refrigerant heater 9 is operated, i.e, gas burner 10 is turned on. As a result, the refrigerant flows in the direction indicated by the broken-line arrows, indoor heat exchanger 6 functioning as a condenser, and refrigerant heater 9 as an evaporator
In the air conditioner shown in FIG. 1, temperature Tc in indoor heat exchanger 6 is detected. FIG. 2 shows changes of temperature Tc. When the detected temperature Tc exceeds set temperature Ts1, the opening of proportional control valve 11 is narrowed, thereby reducing the degree of the combustion in gas burner 10. Thus, release control is performed so that refrigerant heater 9 generates less heat, preventing the pressure in the refrigeration circuit on the high pressure side from rising extraordinarily.
An air conditioner is also known, which can be set in a hot air blow-off mode. In the mode, indoor fan 13 rotates at a low rate, and hot air is blown off indoors, thereby increasing the indoor temperature satisfactorily.
If the above-mentioned air conditioner having the release control function is set in the hot air blow-off mode is set, hot air is blown off at first; however, as shown in FIG. 3, the temperature Tc of indoor heat exchanger 6 rises to a set temperature Ts1 instantaneously, and the release control is started. As a result, refrigerant heater 9 generates less heat, and warmth is not provided to the user. In addition, since the release control is executed and canceled alternately, the indoor temperature varies greatly, the user cannot have sufficient warm. Thus, it is difficult to perform a comfortable heating.